1. Technical Field
The present disclosure relates to a signal processing device that corrects a quadrature error that occurs in quadrature modulation of a signal and a malfunction determining method.
2. Description of the Related Art
In recent years, development of a wireless communication device using quadrature modulation has been rapidly progressing along with miniaturization of a CMOS process in techniques such as millimeter-wave communication using a 60 GHz band and millimeter-wave radar using a 77 GHz to 81 GHz band. When a signal is quadrature-modulated in the wireless communication device, carrier leak and image leak occur due to a differential and a quadrature error. Since a millimeter-wave signal has higher sensitivity to a variation that occurs in a production process and has a larger differential and a larger quadrature error than a conventional microwave band signal, it is difficult for a conventional wireless communication device to suppress carrier leak and image leak.
Japanese Unexamined Patent Application Publication No. 2010-283589 discloses a communication device that quantizes a power envelope signal which is a microwave band transmission wave by using an ADC (Analog Digital Converter) and detects a frequency component thereof by using FFT (Fast Fourier Transform).
One example of means for suppressing carrier leak and image leak is application of the arrangement disclosed in Japanese Unexamined Patent Application Publication No. 2010-283589. However, in Japanese Unexamined Patent Application Publication No. 2010-283589, it is difficult to detect a signal whose level is below a detection limit of the ADC, and it is therefore difficult to distinguish a case where the level of a quadrature error falls below the detection limit due to proper correction of the quadrature error and a case where the quadrature error is not detected because of malfunction of a power detector and peripheral circuits thereof that correct the quadrature error.